I'm using version 2.0.9. @jymboche when you access the content of $qb->Office->something. How many SQL is executed behind the scenes !?
In my case, when I do this kind of thing, for each result (that I access this way $aModel->anotherModel) behind the scenes a SELECT is executed to get data from another model. That was the point of the question.

In futher study, I noticed that I was misunderstanding the use of Models.

"If you want to access $aModel->AnotherModel->somePropertie of course you want all the data of AnotherModel."

For listing purposes, on a table for example, you may not need all the data from the related model. So:

Thanks @Jurigag. I understood at the end what phalcon does behind the scenes, and it really makes sence. By trying to access the robot.RobotBrand I`m saing "hey give me all the data from RobotBrand". But thanks, this answers the question.